Re: [Swig-user] Problem of directors in C++ -> Csharp

[David P. <dpi...@me...>]

This is normal behavior for SWIG C#. The problem is that SWIG has to convert the pointer returned by the getLastInserted function into a C# object, and it has no idea that a C# object already exists, so it creates a wrapper of type Obj to represent the pointer. Note that this problem exists whenever a C++ function returns a derived-class object in a base-class pointer, regardless of whether directors are involved. On the plus side, you can still call the virtual function fn() through the new wrapper. But I don't know if anyone has developed a workaround for this problem. Sorry.

From: Giorgio Scorzelli [mailto:scr...@co...]
Sent: Tuesday, October 06, 2009 11:03 AM
To: swi...@li...
Subject: [Swig-user] Problem of directors in C++ -> Csharp

This is a very simple example of the problem I'm having with Swig directors

///////////////////////////
in C++
////////////////////////

class Obj
{
public:
        Obj() {...}
        virtual void fn() {...}
};

class Container
{
        [...]
public:
         Container();
        void insert(Obj* obj);
        Obj* getLastInserted();
};

///////////////////////////
in Swig
///////////////////////////

%feature("director") Obj;

///////////////////////////
in CSharp
///////////////////////////

class CsObj: Obj
{
        CsObj() {...}
        public override void fn() {...}

};

static void Main()
{
        Container c=new Container();

        CsObj o1=new CsObj();
        o1.fn(); //OKvirtual is working

         c.insert(o1);

        CsObj o2=(CsObj)c.getLastInserted(); //ERROR HERE!!!!
}

I'm sure the object returned by getLastInserted is a CsObj,
but .NET produce an error (impossible to cast).

The strange thing is that the same example is perfecly working in Swig/Python!

Do you have any idea how to solve the problem?
Basically I need to get back the C# class.
Thanks.